1. Field of the Invention
The present invention relates to a dynamic radiographic image obtaining method and apparatus for obtaining a dynamic radiographic image of a moving subject. More specifically, the present invention relates to a dynamic radiographic image obtaining method and apparatus for obtaining a dynamic radiographic image of a periodically moving subject.
2. Description of the Related Art
In the field of radiography, such as medical radiography for diagnosis and the like, or industrial radiography for non-destructive inspection for devices and the like, various radiographic image obtaining systems are known. These systems detect the radiation passed through the subject to obtain radiographic image information carried by the radiation as image signals.
For example, if radiation is irradiated on a storage phosphor, a part of the radiation energy is stored, and photostimulated luminescence is emitted in proportion to the energy stored therein when excitation light, such as visible light or a laser beam, is irradiated thereon. A radiographic image obtaining system that uses a storage phosphor sheet made of storage phosphor (photostimulable phosphor) layered on a substrate is widely put into practical use, which is known as computed Radiography (CR). In the system, the radiation passed through the subject, such as a human body, is received by the phosphor sheet to store the radiographic image information carried by the radiation, and excitation light, such as a laser beam is irradiated on the phosphor sheet to produce photostimulated luminescence, which is then converted to image signals through photoelectric conversion.
Another type of radiographic image obtaining system that stores radiographic image information, and reads out the information as image signals is also proposed. The system uses an electrostatic recording medium for recording a radiographic image as a latent charge image. In the system, the radiographic image information is recorded as a latent charge image by storing an amount of charges which is proportional to the radiation dosage irradiated thereon in the storage section of the electrostatic recording medium as the charges forming the latent image, and image signals are read out from the storage section according to the latent charge image. For this type radiation image obtaining system, several different types are proposed. For example, from the aspect of charge reading process, TFT reading system and optical reading system are proposed. TFT reading system converts charges forming a latent image stored in the storage section to image signals by driving TFTs to scan the recording medium, and outputs the converted image signals. Optical reading system converts the charges forming a latent image stored in the storage section to image signals by irradiating a reading electromagnetic wave (generally, visible light), and outputs the image signals.
In addition, several dynamic radiographic image obtaining methods for obtaining a dynamic radiographic image of a moving subject using these radiographic image obtaining systems are proposed by the applicant or others as described, for example, in Japanese Unexamined Patent Publication No. 7(1995)-193751.
In the dynamic radiographic image obtaining apparatus described in Japanese Unexamined Patent Publication No. 7(1995)-193751, however, a large amount of image signals needs to be read out for obtaining a radiographic image having high resolution, which requires a prolonged reading time, so that it is difficult to obtain a multitude of high-resolution radiographic images in a short period of time. Consequently, radiographic images are obtained as low resolution images when a dynamic image is obtained, and as high resolution images only when still images are obtained. Thus, the apparatus has a problem that detailed functional diagnosis by the observer is difficult to perform even if the dynamic radiographic image is displayed as a motion image on the monitor or the like.
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide a dynamic radiographic image obtaining method and apparatus capable of enhancing the resolution of a dynamic radiographic image.